Global coral bleaching event expands, now the largest on record

NOAA reports record coral reef bleaching event, threatening global reefs and ecosystems, prompting urgent UN summit discussions.

The mass bleaching of coral reefs around the world since February 2023 is now the most extensive on record, the National Oceanic and Atmospheric Administration (NOAA) has said.

A staggering 77% of the world’s coral reef areas – from the Atlantic to the Pacific to the Indian oceans – have so far been subjected to bleaching-level heat stress, according to satellite data, as climate change fuels record and near-record ocean temperatures across the world.

“This event is still increasing in spatial extent and we’ve broken the previous record by more than 11% in about half the amount of time,” said NOAA Coral Reef Watch coordinator Derek Manzello. “This could potentially have serious ramifications for the ultimate response of these reefs to these bleaching events.”

The NOAA coral reef authority declared the global bleaching event in April 2024, making it the fourth of its kind since 1998. The previous record from the 2014 to 2017 mass bleaching affected just below 66 percent of the world’s reef area.

Triggered by heat stress in warm oceans, coral bleaching occurs when corals expel the colourful algae living in their tissues. Without these helpful algae, the corals become pale and are vulnerable to starvation and disease. A bleached coral is not dead, but ocean temperatures need to cool off for any hope of recovery.

At least 14% of the world’s remaining corals were estimated to have died in the previous two global bleaching events.

Though this mass bleaching is already the most widespread, affecting reefs in 74 countries and territories, NOAA has so far stopped short of calling, it the “worst” on record. In coming months and years scientists will conduct underwater assessments of dead corals to help tally up the severity of the damage.